WA-SOM ANALYSIS OF MONTH RUNOFF TIME-FREQUENCY COMPREHENSIVE CHARACTERISTICS IN THE LOWER YELLOW RIVER UNDER THE INFLUENCE OF HUMAN ACTIVITIES AND CLIMATE CHANGE
人类活动和气候变化影响下的黄河下游月径流时-频综合特征的小波分析-自组织映射网络(WA-SOM)分析

In recent years,the impact is great of human activities and climate change on runoff especially in Yellow River,because the water resources system of Yellow River is fragile.The Yellow River's zero flow has been becoming one of the most serious environment problems in our country.Taking the 54 year(1950～2003) month runoff series and annual runoff series obtained from Lijin hydrologic station as a basic data and taking 1970 as a demarcation point,a WA-SOM coupling mode was established by comparing the characteristics of month runoff series and annual runoff series of 1950～1969 with those of 1970～2003 to analyze characteristics of the lower Yellow River's runoff.The wavelet analysis (WA) method and the self-organized map (SOM) were used in establishing the model.The results show that for the lower Yellow River after 1970,the month runoff and the annual runoff series decreased significantly,while C_v(coefficient of variation) and C_s(coefficient of skewness) of the month runoff series (except January and December) and the annual runoff series increased remarkably.As a whole,the main periods of month runoff after 1970 became more complex than that of before 1970.After 1970,the change of runoff series of January and February was not obvious,but the change of runoff series of the other months was significant.The runoff series of March,April,May and June became similar,while the runoff series of August,September and October became different.This might be because of the increased water demand by the development of national economy,the overexploitation of groundwater,and changed water cycle by the hydraulic engineering construction.Of course,climate change is also an important factor.